Method of providing an electric lamp envelope with a non-uniform light-diffusing coating



Nov. 15, 1960 D. s. GUSTIN EIAL 2,960,414 7 METHOD OF PROVIDING ANELECTRIC LAMP ENVELOPE WITH A NON-UNIFORM LIGHT-DIFFUSING COATING FiledFeb. 27, 1959 2 Sheets-Sheet 1 Ll-l g. Q N l-Ll I l-l-I 4 D. 5 1 2% w aO 2 O LIJ INVENTORS ATTORN Y Nov. 15, 1960 D TIN EI'AL 60,414

s. GUS 2 METHOD OF PROVIDING AN ELECTRIC LAMP ENVELOPE WITH ANON-UNIFORM ucm nmusmc comma Filed Feb. 27, 1959 2 Sheets-Sheet 2MOISTURE REMOVAL I I l I 9 i "l E 2 I E M INVENTORS DAN/EL 8. GUS 7/ BYll/YK. R085)? 04/ ATTORN Y United States Patent METHOD OF PROVIDING ANELECTRIC LAMP ENVELOPE WITH A NON-UNIFORM LIGHT-DIF- FUSING COATINGDaniel S. Gustin, Saugus, and John K. Robertson, Lynn, Mass., assignors,by mesne assignments, to Sylvania Electric Products Inc., Wilmington,Del., a corporation of Delaware Filed Feb. 27, 1959, Ser. No. 796,038

3 Claims. (Cl. 11-7-9) This invention relates to the manufacture ofelectric lamps and more particularly to the manufacture of electriclamps provided with a coating of light-ditfusing material on the innerwall thereof.

Over the years, various methods and techniques have been employed toprovide for light dilfusion in the manufactur'e of electric lamps. Forexample, in the manufacture of incandescent electric lamps, the mostcommon light-diffusing bulb has been the inside frost, Le, a bulb inwhich the interior surface has been frosted by etching. Another approachto providing a light-diffusing bulb for an electric lamp has been theapplication of a coating of light-diffusing material to the inside wallof a lamp envelope. Various techniques have been employed to effect theapplication of this light-diffusing ma terial. In some cases thelight-diffusing material is suspended in a binder, the suspension isapplied to the lamp envelope, and the binder burned olf to leave thedesired coating. In other cases the light-diffusing material has beensmoked onto the inner wall of the'lamp envelope as taught in US. Patent2,545,896 to Pipkin. In still other cases, the light-(infusing materialhas been electrostatically precipitated onto the inner wall of the lampenvelope by some suitable means, for example, such as taught in theco-pending application of Daniel S. Gustin, Serial Number 575,111, filedMarch 30, 1956, entitled Method of Coating Electric Lamp Envelopes, nowU.S.

Patent 2,878,136, issued March 17, 1959.

In the manufacture and sale of incandescent lamps of the types and sizesnormally found in the home, and in some commercial applications, asubstantial interest has been exhibited in the provision of a lamp inwhich certain areas of the lamp envelope are provided with a coating oflight-difiusing material and other areas are uncoated. In someinstances, this interest stems from utilitarian considerations and inothers from aesthetic considerations.

In view thereof, a principal object of this invention is to provide anelectric lamp in which some portions of the lamp. envelope are coatedwith a light-dilfusing material vhile other portions of the same lampenvelope are uncoated.

Another object is to provide a relatively inexpensive method providingthese coated and uncoated areas on the inner wall of a lamp envelope.

A further object is to provide a coating method which readily lendsitself to adaptation to conventional highspeed lamp manufacturingequipment.

The patent art is not devoid of suggestions for masking a portion of alamp envelope while the remainder thereof is being provided with acoating. For example, US. Patent 2,855,326, which issued October 7,1958, teaches a method of masking a portion of a reflector lamp envelopewhile a coating of reflective material is being applied to the remainderof the lamp envelope.

'However, the teachings of this patent and others of similar nature donot readily lend themselves to adapta- 2,960,414 C Patented Nov. 15,1960 tion to conventional high-speed equipment'employed in themanufacture of incandescent lamps of the types and sizes underconsideration.

In. accordance with the principles of this invention, a substantialtemperature differential is effected between certain areas of a lampenvelope, the inner wall of which has been provided with a coating oflight-diffusing material. The coating is then exposed to a very humidatmosphere, such as steam for example. The steam will condense on thecooler areas of the lamp envelope and effect a setting of the coating inthese areas. The lamp envelope, particularly the areas on which thesteam has condensed is then heated to remove this moisture. Finally ablast of air is introduced into the lamp envelope and directed againstthe areas which have been heated prior to steaming, thereby removing thecoating of light-difiusing material from these areas. The sequence ofsteps in the practice of the method of this invention is illustrated inthe accompanying drawings in which:

Figure 1 is an elevational view of a lamp envelope seated on a suitablesupport or head. The lamp envelope of Figure 1 has a coating oflight-diffusing material on the interior wall thereof down to thecut-oli line on the neck thereof.

Figure 2 is a view similar to Figure 1, showing a bushy fire heating thetop of the bulbous portion of the lamp envelope.

Figure 3 is a view similar to Figure 2, showing a sharp fire directedonto the lamp envelope along a line which is' to be the coating cut-offline.

Figure 4 is a view similar to Figure 1 but with the lamp envelope brokenaway to show that portion of the head assembly disposed therein. Thelamp envelope is steamed at this point.

Figure 5 is a view similar to Figure 4. The lamp envelope is heated toremove the moisture at this point.

Figure 6 is a view similar to Figure 5. At this point the lamp envelopeis securely held in position on the head and a blast of air isintroduced to remove a portion of the light-diffusing coating.

Although, in the specific embodiment of the invention illustrated in theaccompanying drawings and described below, reference is made to anelectrostatic precipitation technique for applying a coating oflight-diffusing material to the inner wall of an electric lamp envelope,it should be understood that the method of this invention may bepracticed in cases where other techniques are employed to effect theapplication of the coating of lightdiffusing material.

The lamp envelope 1 of Figure 1, seated on a rotatable bulb-supportinghead 2, may be provided with a coating of light-diffusing material onthe inner wall thereof in the manner taught in the co-pendingapplication of Daniel-S. Gustin, Serial Number 575,111, filed March 30,1956, now US. Patent 2,878,136, issued March 17 1959. In accordance withthe teaching of that application, the light-diflusing medium iselectrostatically precipitated onto the inner wall of the lamp envelopefrom a stream of air in which the medium is suspended, the coatingextending down to the neck cut-off line 5. Further, in accordance withthe teaching of that application, the light-dififusing materialcomprises a mechanical powdered mixture of a material selected from thegroup consisting of wollastonite and bone ash, and a material selectedfrom the group consisting of silicon dioxide and aluminum oxide beingbetween about 1% and about 15% by' weight of the said first saidmentioned material and having an average particle size below a micron.However, before the coating is exposed to a very humid atmosphere, suchas steam for example, in order to set the area 3 should not be heated toa temperature so high that the remainder of the lamp envelope will beheated substantially by radiation. It. has been found that satisfactoryresults are obtained when the temperature range is between about 225 F.to about 300 F.

As shown in Figure 3, a sharp fire 8 from burner 10' is directed ontothe rotating lamp envelope to define the cut-off line 12 if a sharpcut-01f is desired.

Immediately after these heating operations have been effected, steam isintroduced into the lamp envelope through tube 10 which is projectedthrough a bore provided therefor in the head 2 (Fig. 4). The steamcondenses on the cooler areas of the bulb, thereby effecting a settingof the coating as taught in the referenced Gustin application. However,the steam does not condense on the area 3 from which it is desired toremove the coating because of the heating of this area as aforesaid.

After the lamp envelope has been steamed, it is heated to bake out andremove the moisture introduced during steaming. This may be done, forexample, by introducing a gentle flow of hot air into the lamp envelopethrough tube 13 (Fig. 5) which is projected through a bore providedtherefor in the head 2. External heating means may also be employed toeffect this drying. Thereafter, a suitable bulb retaining means 14 islowered into firm, frictional engagement with the top of the lampenvelope and a stream of a gas, such as air under pressure, isintroduced into the bulb through a tube 16 (Fig. 6) and directed againstthe area 3 to displace the coating therefrom, the line 12 defining asharp cut-off between the coated and un-coated portions of the lampenvelope.

Although the specific example of the method of this invention has beenillustrated and described in connection with the electrostaticprecipitation technique for providing the inner wall of an electric lampenvelope with a coating of a light-diffusing material, as indicatedabove, the method may also be practiced with other coating techniques.For example, when the coating material is suspended in a binder, thesuspension is applied and the binder if burned off, leaving the desiredcoating. In the application of the method of this invention to thesuspension coating technique, the suspension coating technique is notaltered in anyway. Subsequent to the step of burning off of the binderin the suspension coating technique, the coating is steamed, the areafrom which coating is to be removed is heated, etc., as taught above.

In the specific example of the method of this invention, coating isremoved from the top of the bulbous portion of the lamp envelope. It hasbeen found that when the coating of light-diffusing material has beenremoved from a frosted bulb in the area illustrated in the accompanyingdrawings, an increase of about 15% in the downward component of light isobtained over the downward component of light from an ordinary frostedbulb. Thus lamps made in'accordance with the teachings of this methodpossess significant practical advantages in installations where thedownward light component is the primary consideration.

It will be readily apparent to those skilled in the art that areas ofthe lamp envelope other than or in addition to the area described aboveand illustrated in the accompanying drawings may be treated inaccordance with the principles ofthis invention. For example, a sharpfire could be used to trace a design of desired configuration on thelamp envelope. Suitabl external 4 l shielding means may be disposed inproximity to or in engagement with the outer wall of the lamp envelopein register with the areas from which coating is to be removed and theseareas heated as described above. Multi-colored coatings may also beprovided by coating with one color, removing the coating from certainareas and then applying a second coat which will be most promi nent inthe area from which the first coating was removed.

Although the method of this invention has been described as moreparticularly related to the manufacture of electric lamps provided witha coating of light-diffusing material, it will be readily understood bythose skilled in the art that it may also be practiced in themanufacture of electric lamps provided with other types oflight-modifying materials, such as light-reflecting and light-absorbingmaterials for example.

What we claim is: r

1. The method of treating an electric lamp envelope provided with acoating of light-diffusing material on the inner wall thereof, saidcoating being of the type which adheres more tenaciously when steam isapplied thereto, said method comprising: heating a selected portion ofthe lamp envelope to a temperature between about 225 F. to about 300 F.;introducing steam into the lamp envelope whereby the said coating isexposed thereto, the steam condensing on the cooler portions of the lampenvelope and effecting a setting of the coating thereon; heating thelamp envelope to remove the moisture introduced therein during steaming;and directing a stream of gas under pressure against the first mentionedheated selected portion of the lamp envelope whereby the coating on saidselected portion is removed therefrom.

2. The method of treating on electric lamp envelope provided with acoating of light-diffusing material on the inner wall thereof, saidcoating being of the type which adheres more tenaciously when steam isapplied thereto, said method comprising: heating a selected portion ofthe lamp envelope to a temperature between about 225 F. to about 300 F.;introducing steam into the lamp envelope whereby the said coating isexposed thereto, the steam condensing on the cooler portions of the lampenvelope and effecting a setting of the coating thereon; heating thelamp envelope to remove the moisture introduced therein during steaming;and directing a stream of air under pressure against the first mentionedheated selected portion of the lamp envelope whereby the coating on saidselected portion is removed therefrom.

3. The method of treating an electric lamp envelope provided with acoating of light-diffusing material on the inner wall thereof, saidcoating being of the typewhich adheres more tenaciously when steam isapplied thereto,

said method comprising: heating a selected portion of the lamp envelopeto a temperature between about 225 F. to about 300 F.; directing a sharpfire along the line of demarcation between said selected portion and theremainder of said lamp envelope; introducing steam into the lampenvelope whereby the said coating is exposed thereto, the steamcondensing on the cooler po tions of the lamp envelope and effectingasetting of the coating thereon; heating the lamp envelope to remove themoisture introduced therein during steaming;- and directing a stream ofgas under pressure against the first mentioned heated selected portionof the lamp envelope whereby the coating on said selected portion isremoved therefrom.

Rea ent; Cited in the file of this patent.

UNITED STATES PATENTS 2,151,686 Briefer Mar. 28, 1939 2,837,440 BoivinJune 3, 1958 2,877,139 Hyde Mar. 10, 1959 ,878, 36 Gustin Mar. 17, 1959

1. THE METHOD OF TREATING AN ELECTRIC LAMP ENVELOPE PROVIDED WITH ACOATING OF LIGHT-DIFFUSING MATERIAL ON THE INNER WALL THEREOF, SAIDCOATING BEING OF THE TYPE WHICH ADHERES MORE TENACIOUSLY WHEN STEAM ISAPPLIED THERETO, SAID METHOD COMPRISING: HEATING A SELECTED PORTION OFTHE LAMP ENVELOPE TO A TEMPERATURE BETWEEN ABOUT 255* F. TO ABOUT 300*F,INTRODUCING STEAM INTO THE LAMP ENVELOPE WHEREBY THE SAID COATING ISEXPOSED THERETO, THE STEAM CONDENSING ON THE COOLER PORTIONS OF THE LAMPENVELOPE AND EFFECTING A SETTING OF THE COATING THEREON, HEATING THELAMP ENVELOPE TO REMOVE THE MOISTURE INTRODUCED THEREIN DURING STEAMING,AND DIRECTING A STREAM OF GAS UNDER PRESSURE AGAINST THE FIRST MENTIONEDHEATED SELECTED PORTION OF THE LAMP ENVELOPE WHEREBY THE COATING ON SAIDSELECTED PORTION IS REMOVED THEREFROM.